Simple high-performance single-turn potentiometer

ABSTRACT

A simple one-turn potentiometer having a housing, an adjustment shaft molded in place in the housing, a rotary ceramic chip element on the interior end of the shaft to give high heat dissipation, and integral contact and terminal members molded in place in the end cap with contacts on the interior of the housing and juxtaposed to brush on a shaft-carried disc and with terminals exposed on the rear exterior.

United States Patent Inventor Frank J. Bruder Newport Beach, Calif.25,704

Apr. 6, 1970 Apr. 27, 1971 Bourns, Inc.

Appl. No. Filed Patented Assignee SlMPLE HIGH-PERFORMANCE SINGLE-TURNPOTEN'IIOMETER 7 Claims, 6 Drawing Figs.

US. Cl 338/150, 3 38/ 159 int. Cl. ll0lc 9/02 Field of Search .1338/150,

[56] References Cited UNITED STATES PATENTS 2,480,218 8/1949 Bumell338/159 2,862,088 11/1958 Mairs 338/164X Primary Examiner-Lewis H. MyersAssistant Examiner-D. A. Tone AttorneyFritz B. Peterson ABSTRACT: Asimple one-turn potentiometer having a housing, an adjustment shaftmolded in place in the housing, a 1'0- tary ceramic chip element on theinterior end of the shaft to give high heat dissipation, and integralcontact and terminal members molded in place in the end cap withcontacts on the interior of the housing and juxtaposed to brush on ashaft-carried disc and with terminals exposed on the rear exterior.

PATENTED mm ISL-576,510

M/VEA/TO/Q FRANK J. BRUDER SIMPLE HIGH-PERFORMANCE SINGLE-TURNPOTENTIOMETER BRIEF SUMMARY OF THE INVENTION l. The Prior Art in thefield of potentiometers in which this invention reposes', it is usual toproduce a potentiometer comprising a or enclosure of two or nrore partsor members to enclose and protect the operating components, toincorporate in the principal housing member a bushing or bearing forreception of a rotary actuating shaft, to mount in the housing aresistance element and a return conductor, and to mount on the in thehousing, a rotary contact usually retained in a plastic rotor attachedto the shaft to brush on the resistance 1 element incident to rotationof the shaft. Provisions are made for. electrical connections, usuallyin the form of terminal I members affixed on or in one of the housingmembers and connected, as by means of solder, wires, or rivets, torespective ends of the resistance element and the return conductor. Suchpotentiometer constructions entail much labor in assembling andadjusting the components, and involve a relatively large number ofparts. Additionally, in the absence of added special means, suchconstructions are of limited electrical power ratingbecause of inabilityto accommodate the large amount of. heat generated when appreciablecurrent passes through the element. The bushing, which pennits thepotentiometer to be affixed to a panel and which serves as a bearing in,an externally threaded protrusion fomred integrally with one moldedmember of the housingby the shaft being molded in place. in that member.Thusgmanual assembly of those two avoidedwith considerable reduction inthe clearance between the. parts; and the retaining ring or the like iseliminated. Further, rather than affixing the resistance element tothehousing, that element, in accordwith this invention, is mounted on anelectrically insulative heat-conducting ceramic carrier that is directlyattached to the adjusting shaft. Thus heat israpidly conducted away fromthe resistance elementvia the ceramic carrier to the shaft from which itis readily radiated and/or conductively removed both through the normalmounting panel and the knob. As a consequence, the

heat dissipation, temperature rating, and resistance stability of thepotentiometer are grossly improved. Additionally, in accord with theinvention, the contact devices are each made integral with the,respectivev tenninal, thus forming what are herein in instances termedterminal-contact members; and as-- sembly of contacts to a rotor andsoldering or spotwelding of connections are concurrently avoided oreliminated by molding the terminal-contact members in place in a moldedhousing member which conveniently may be the cap or cover piece of thehousing. The terminal contact members are preferably I made of amaterial which hardens and gains resiliency when cold-worked, whichmaterial can be coined, and which does not require plating orothertreatment generally requiredfor facilitating soldering..Theterminal-contact members are thus I very simply formed, and by shearingand coining contact fingers and shaping and bending them, they arerendered resilient although fonned from material which initially ispreferably in annealed condition. Further the terminal-contact membersare so arranged as to occupy only a very small space, are initiallyexposed to view to permit easy adjustment and inspection, and are lockedin position with no possibility of displacement due to vibration orshock. The terminal-contact members are preferably formed from annealedworkhardenable alloy, such as, for example, ASTM-B 1 22-60 Alloy 4,containing 55percent copper, 27percent zinc and l8percent nickel. Itwill be herein made evident that no manual assembly of the terminals,nor the contacts, is required. The above-detailed novel features permiteasy and inexpensive construction of a high-rating reliablepotentiometer of minimum volume from only seven members, it beingconsidered that the ceramic base and resistance element constitute asingle member.

As illustrated herein in a preferred form, the resistance element is aoennet film formed on one face of a preferably circular ceramic waferwhose central aperture receives a reduced diameter short section of theinner end of the adjusting shaft; and the wafer is rigidly secured tothe shaft by peening over the inner end of the short section of theshaft. Additionally, adhesive. may also be utilized if desirable.Conveniently and most effectively, the principal or body memberof thehousing is formed as a shallow cup-shaped body with a threadedprotrusion at its exterior, and with an upstanding projection protrudingfrom the interior bottom of the cup, whereby to fonn arotation limitingdevice herein termed a fixed stop. The ceramic wafer similarly isprovided with a complementary protrusion or abutment on the faceopposite from the cermet element, which abutment is herein termed arotary stop. The stop devices thus provided are dimensioned so thatrotation of the adjusting shaft is limited to that necessary to carrythe entire length or extent of the arcuate resistance element past thecontact points of the respective terminal'contact member. As will bemade evident, each terminal-contact member is fonned, for example, froma strip of resilient material, and with-a plurality of resilient fingersorlimbs at its inner end, with each finger tenninating in a contactpoint that engages with one of the active (resistive or conductive)components on the rotary ceramic wafer. Thus contact-resistancevariation (CRV) and contact noise in the electrical sense are minimized.

The foregoing brief general description of the invention makes itevident that it is a principal broad object of the invention to providean exceptionally inexpensive potentiometer characterized by highelectrical rating.

Another object of the invention'is to provide a potentiometerconstruction with superior ability to rapidly dissipate heat that may begenerated in the resistive element.

Another object of the invention is to provide a simple procedure formanufacturing a potentiometer.

Another object of the invention is to improve the precision ofconstruction and operation of a potentiometer while concurrentlysimplifying assembly of the potentiometer.

Other objects and advantages of the invention are hereinafter set forthor made evident in the appended claims and the following detaileddescription of the presently preferred illustrative embodiment of theinvention illustrated in the appended drawings.

DESCRIPTlON OF THE DRAWINGS element device comprised in thepotentiometer illustrated in FlGS. l and 2, showing a centrallyapertured ceramic wafer of disc form carrying an arcuate cermetresistance element with conductive terminations and collectors of filmform;

H6. 4 is an inner face view of a second or subsidiary housing member inthe form of a cover or cap with three moldedin-place terminal-contactmembers, the scale being approximately the same as that used in FIG. 3;

FIG. 5 is a longitudinal axial cross-sectional view of the exemplarypotentiometer, on a considerably enlarged scale, illustratingconstructional features; and

FIG. 6 is an end view of the principal housing member and molded-inrotary shaft of the exemplary potentiometer, viewed from the cap orterminal end, prior to addition of the ceramic wafer and cap, the scalebeing approximately the same as that chosen for FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION I lubricating characteristics areconcurrently attained. The cap member 24 is preferably formed of diallylphthalate whereby excellent resistance to physical abuse and temperatureeffects is attained, with compatibility with the material of which bodymember 22 is formed. Both of the members are electrically insulative.

The first housing member 22 is molded around a rotary adjusting shaft26, fabricated of aluminum alloy such as alloy 201 I-T3. The shaft isprovided with at least one section 26a (FIG. 5) of reduced diameterwithin the molded-in portion of its length, whereby the shaft is heldcaptive by member 22 but is rotatable about its axis therein. To insurethat the shaft is rotatable in the encircling housing member 22, theshaft is initially coated with a film of a mold-release material, suchas a silicone compound well known in the molding arts, prior to themolding operation. As indicated, the reduced-diameter intermediateportion 26a of the shaft is thus rotatably enclosed or situated in anexteriorly threaded cylindrical protuberance 22a formed as an integralpart of member 22; and an externally exposed actuator-receiving portion26b of the shaft is left protruding from member 22, whereby ashaft-rotating means such as a knob or other driver may be applied tothe shaft for facilitating rotation.

The inner or rear end of shaft 26 is provided during its manufacturewith an annular face 260 (FIG. 5) and a portion of reduced diameterforming a seat 26d, which face and seat serve as supporting andpositioning means upon which is received and held an insulative wafer28w comprised in the device 28. The shaft 26 is counterbored at itsinner end, as indicated at 26c, to provide a deformable circular edgeportion which is spun or pressed outwardly and tightly against thesurface of wafer 28w as indicated at 26f. The wafer is thus firmlysecured to the inner end of the shaft, so as to be rotatable therewithwithout slipping or other relative motion therebetween.

As is indicated in FIGS. 2 and 3, the rotary resistance element device28 comprising the insulative ceramic wafer 28w carries on its rear facean outer annular conductive film 28a and an inner annular conductivefilm 28b encircling but spaced radially outwardly from the centralaperture 28c. The films are produced by applying on the wafer, by silkscreen or like means, a conductor'containing ink or paste such as silverink, and firing the wafer to reduce the ink to a metal film, in a mannerwell known in the ceramics art. Disposed between films 28a and 28b onthe rear face of the wafer 28, but separated therefrom between its ends,is an arcuate resistance element zse. While the element 284: is hereinshown and described as a comet element whereby high current ratings areaccommodated, it is evident that other types of thin-film resistanceelements may be used in certain applications of the principles of theinvention. The arcuate element 28a is electrically connected at one endthereof to the outer conductive annulus 280 by an inward extension 28aof the latter which overlies or underlies the end portion of the elementand forms a conductive termination for the element. Similarly theelement 28c is electrically connected at the other end thereof to theinner conductive annulus 28b by a termination 28b. The terminations arepreferably integral with and concurrently formed with the respectivefilms 28a and 28b.

The preceding description makes it evident that as the shaft 26 isrotated, within limits hereinafter explained, the element 28e will betraversed in a circular path past a specific station at which it may bebrushed by a set of one or more fixed contact points.

The second housing member, 24, is molded as a platelike disc that isshaped and dimensioned to fit securely on the rim 22r (FIG. 2) of thecup portion of housing member 22, and to be secured and sealed theretoby adhesive. means and to thereby form in conjunction with member 22 aclosed chamber C (FIG. 5). To aid in easy attachment of cap member 24 tothe complementary rim of member 22, the latter is produced with inwardlyprojecting lugs such as 22m (FIG. 2), and member 24 is formed withcomplementary recesses such as 24m into which the lugs enter and seat asthe cap is brought against the rim 22r and rotated. The periphery of thecap 24 is formed with a flange 24f against which rim 22r is devised toseat, and seating is as indicated in FIG. 5.

Incorporated into the cap member 24 of the housing by insert-moldingtechniques is a set 30 (FIG. 2) of terminal contact members which are,for example, fabricated from 0.012 inches thick annealed 18 percentnickel silver. As is indicated in FIGS. 4 and 5, the exterior face ofthe cap is depressed to expose a portion of each of the terminal-contactmembers so that each of those members has an outer exposed end that canbe bent out rearwardly or left as shown; the members thus forming orproviding electrical terminals 32, 34 and 36. Each such member has itsother or inner end coined to achieve approximately 0.004 inchesthickness and a hardness equal to spring temper, and each is furtherdeformed to provide a respective one of sets of contact fingers, 32c,34c, and 36c. The ends of the contact fingers 32 provide contact points32c (FIG. 5) that are positioned to contact or brush on the innercollector 28b, and similarly the fingers 34 provide points 34cpositioned to brush on the resistance element 28e. A similar set ofcontact points at the ends of the contact fingers 36c are positioned tocontact or brush on the annular conductive return or collector 28a. Thegeneral positioning and interrelationships of the films and contactpoints are as indicated in FIG. 5 with respect to the fingers 32c andcontact points 32c.

To limit rotation of the rotor assembly comprising shaft 26 and wafer 28so as to restrict brushing of contact points 34c" to the extent ofelement 28c between the terminations 28a and 28b, the wafer is producedor formed with a protruding rotary stop abutment 28s (FIGS. 3 and 5) onits face opposite the conductive and resistive films 28a, 28b and 28a;and the inner face or floor of housing body member 22 is produced withan outstanding fixed stop abutment 22s (FIG. 6), both ends of which areadapted to arrest the rotary stop abutment 28s at a respective extremeof movement of the latter. Thus as rotation of the shaft 26 is continuedin one direction, the rotary stop abutment 28s is arrested by one endface of the fixed stop 22: and one electrical end of element 28c iscontacted by points 340'; and as the rotation is continued in theopposite direction, the abutment 28s is arrested by the other end faceof stop 22s and the other electrical end of the element 28s is contactedby points 340'. The element is adjusted by rotation of the shaft to aposition intennediate the noted extremes to bring the resistance (orpotential) exhibited between terminal 34 and a selected one of the otherterminals to the desired value.

To aid in securing the potentiometer in an aperture in a panel I(indicated in phantom form in FIG. 5), the body member 22 is providedwith a tang 22t (FIG. 2) that is adapted to be received in a small holeappropriately bored in the panel,

in a manner known in the art. Also, the portion 22a of the body memberis threaded, as indicated, for reception of fastener means such as alockwasher and a nut. The thread 5 may be formed by a threading tool,but is preferably produced during the molding operation.

it is evident from the foregoing description that the noted objects havebeen attained. By forming the resistance element on a highlyheat-conductive ceramic disc finnly secured to a highly heat-conductiveshaft extending to the ambient, heat dissipation is greatly facilitatedand the potentiometer can be given a higher than ordinary operationalrating. By forming the terminals and contacts of soft work-hardenablealloy and coining the contact fingers and points, the latter are giventhe resilience required and thus the formation and connection ofseparate terminals is obviated. Also, by forming the contact fingerswith the respective terminals, and embedding or molding-in theterminals, a plurality of individual assembly operations and contactadjustments previously necessary have been eliminated and obviated. Bymolding the shaft in place in the principal housing member, somepreviously necessary assembling operations and parts, such as retainermeans, have been made unnecessary and have been obviated or eliminated.Thus the potentiometer is much simpler than prior-art potentiometers ofits class, and less expensive to produce. Further, high-performancecharacteristics are attained by the excellent heat-dissipating capacityprovided and by the precision with which the assembly, as of the contactfingers and points, may be effected by the machinery used in molding thehousing members.

Having described in detail the construction and assembly of a preferredform of the invention, it will be evident to others that features of theinvention may vary in form and be used in potentiometers of other thanthe preferred illustrated form, and hence tion therewith; and

fourth means, including a plurality of sets of resilient contact fingerssupported by said housing means, one of said sets having contact pointscontacting said resistance element and another of said sets havingcontact points contacting said return conductor means,

whereby upon rotation of said shaft said resistance element is rotatedpast said one of said sets of spring contact fingers and the pointsthereof and varies the electrical resistance exhibited between said oneset and said other set of contact fingers.

2. A potentiometer as defined in claim 1, in which said first housingmember is of molded construction and said shaft has an intermediateportion rotatable in and retained in said first housing member by thelatter being molded therearound, whereby usual parts and assemblyoperations are unnecessary.

3. A potentiometer as defined in claim 1, in which each of said sets ofresilient contact fingers is integral with a respective conductiveterminal member secured to and protruding from said second housingmember by having an intermediate portion thereof molded in place in saidsecond housing member, whereby usual parts and assembly operations areobviated and made unnecessary.

4. A potentiometer according to claim 3, in which at least one of saidsets of resilient contact fingers is fonned of workhardening alloywhereby required resilience of said fingers is attained by operationsinexpensively performed upon a soft easily worked alloy.

5. A potentiometer according to claim 1, m which said means supportingsaid resistance element is a ceramic wafer, and in which said wafer issecured to said shaft in good heatconductive relation thereto, wherebyoptimum heat dissipation from said element is attained.

6. A potentiometer according to claim 5, in which said sets of resilientcontact fingers are integral with respective conductive terminals ofsoft work-hardenable alloy and in which each of said terminals ispermanently embedded in said second housing member.

7. A potentiometer according to claim 6, in which said wafer and saidhousing means comprise respective ones of movable and fixed stop meansfor restricting rotation of said wafer to the extent necessary toprevent rotation of either end of said resistance element past thecontact points brushing thereon.

1. A potentiometer comprising: first means, including housing meansincluding first and second insulation housing members; second means,including an actuating shaft rotatably mounted in said first housingmember; third means, including an arcuate resistance element and returnconductor means therefor and means supporting said element and conductormeans on said shaft for rotation therewith; and fourth means, includinga plurality of sets of resilient contact fingers supported by saidhousing means, one of said sets having contact points contacting saidresistance element and another of said sets having contact pointscontacting said return conductor means, whereby upon rotation of saidshaft said resistance element is rotated past said one of said sets ofspring contact fingers and the points thereof and varies the electricalresistance exhibited between said one set and said other set of contactfingers.
 2. A potentiometer as defined in claim 1, in which said firsthousing member is of molded construction and said shaft has anintermediate portion rotatable in and retained in said first housingmember by the latter being molded therearound, whereby usual parts andassembly operations are unnecessary.
 3. A potentiometer as defined inclaim 1, in which each of said sets of resilient contact fingers isintegral with a respective conductive terminal member secured to andprotruding from said second housing member by having an intermediateportion thereof molded in place in said second housing member, wherebyusual parts and assembly operations are obviated and made unnecessary.4. A potentiometer according to claim 3, in which at least one of saidsets of resilient contact fingers is formed of work-hardening alloywhereby required resilience of said fingers is attained by operationsinexpensively performed upon a soft easily worked alloy.
 5. Apotentiometer according to claim 1, in which said means supporting saidresistance element is a ceramic wafer, and in which said wafer issecured to said shaft in good heat-conductive relation thereto, wherebyoptimum heat dissipation from said element is attained.
 6. Apotentiometer according to claim 5, in which said sets of resilientcontact fingers are integral with respective conductive terminals ofsoft work-hardenable alloy and in which each of said terminals ispermanently embedded in said second housing member.
 7. A potentiometeraccording to claim 6, in which said wafer and said housing meanscomprise respective ones of movable and fixed stop means for restrictingrotation of said wafer to the extent necessary to prevent rotation ofeither end of said resistance element past the contact points brushingthereon.